Complexation and removal of mercury from flue gas desulfurization systems

ABSTRACT

A method for the reduction and prevention of mercury emissions into the environment from combusted fossil fuels or other off-gases with the use of peracetic acid is disclosed. The peracetic acid is used for the capture of mercury from the resulting flue gases using a flue gas desulfurization system or scrubber. The method uses peracetic acid in conjunction with a scrubber to capture mercury and lower its emission and/or re-emission with stack gases. The method allows the use of coal as a cleaner and environmentally friendlier fuel source as well as capturing mercury from other processing systems.

TECHNICAL FIELD

This invention relates to the reduction of mercury emissions into theenvironment from the combustion of coal and/or other carbon-based fuelsas well as from other processing systems. The invention relates to themethod of capturing mercury from flue gases by flue gas desulfurizationsystems or scrubbers thereby reducing the levels of toxic mercury, whichenables the use of coal as a clean and environmentally friendlier fuelsource as well as makes other processing systems more environmentallydesirable.

BACKGROUND

The demand for electricity continues to grow globally. In order to keepstride with the growing demand, coal continues to be a primary sourcefor electricity generation. The burning of coal in power generationplants results in the release of energy, as well as the production ofsolid waste such as bottom and fly ash, and flue gas emissions into theenvironment. Emissions Standards, as articulated in The Clean Air ActAmendments of 1990 as established by the U.S. Environmental ProtectionAgency (EPA), requires the assessment of hazardous air pollutants fromutility power plants.

Conventional coal-fired combustion furnaces and similar devices produceemissions that include pollutants such as mercury. Mercury vapor cancontribute to health concerns. At the levels common in the atmosphere,the concentrations of mercury are usually safe. However, mercury canaccumulate in ecosystems, for example, as a result of rainfall. Someconventional systems attempt to control mercury emissions withparticulate collection devices.

The primary gas emissions are criteria pollutants (e.g., sulfur dioxide,nitrogen dioxides, particulate material, and carbon monoxide). Secondaryemissions depend on the type of coal or fuel being combusted but includeas examples mercury, selenium, arsenic, and boron. Coal-fired utilityboilers are known to be a major source of anthropogenic mercuryemissions in the United States. In December of 2000, the EPA announcedits intention to regulate mercury emissions from coal-fired utilityboilers despite the fact that a proven best available technology (BAT)did not exist to capture or control the levels of mercury released bythe combustion of coal. This has been further complicated by the lack ofquick, reliable, continuous monitoring methods for mercury.

Mercury (elemental symbol Hg) is a metal that melts at 234K (−38° F.)and boils at 630K (674° F.). As such, it can be expected to have a highvapor pressure relative to many metals. The oxidized forms of mercury,Hg²⁺ and Hg⁺, have much lower vapor pressures and can be captured by flyash particulates.

Mercury is found in coals at concentrations ranging from 0.02 to 1 ppm.The mercury is present as sulfides or is associated with organic matter.Upon combustion the mercury is released and emitted into the flue gas asgaseous elemental mercury and other mercury compounds. The mercuryappears in the flue gas in both the solid and gas phases(particulate-bound mercury and vapor-phase mercury, respectively). Theso-called solid-phase mercury is really vapor-phase mercury adsorbedonto the surface of ash and/or carbon particles. The solid-phase mercurycan be captured by existing particle control devices (PCDs) such aselectrostatic precipitators (ESPs) and fabric filters (FF), the lattersometimes referred to as baghouses.

Several control strategies have been developed for the control ofmercury emissions from coal-fired boilers. Some of these methods includeinjection of activated carbon, modified activated carbon, variouschemical catalysts, and inorganic sorbents. Unfortunately, none of thesestrategies removes all the mercury from the flue gas. The efficienciesrange from as low as 30% to as high as 80% based on the amount ofmercury entering the system with the coal. In addition, thesetechnologies either produce unwanted effects on by-products such asimpacting the quality of fly ash, or they generate additional wastestreams for the power plant. Both lead to higher operational costs forthe power plant. One promising strategy is to take advantage of existingair pollution control devices (APCDs) to augment or to serve as theprimary means to remove vapor-phase mercury. Two examples of APCDs aresemi-dry and wet scrubbers or flue gas desulfurizers (FGD). Semi-dryFGDs are also known as spray dryer absorbers (i.e., SDAs), circulatingdry scrubbers (CDS), or TURBBOSORP® available from Von Roll.

Sulfur oxides (SO_(x)) regulatory compliance mandates the use of atleast one of several control strategies. Three such strategies that areused in the US are sorbent injection into the flue gas following by aparticulate collection device such as an ESP or a FF, and wet or dryflue gas desulfurizers. At present, about 3% of the coal-fired powerplants are using sorbent injection. FGD scrubbing accounts for 85% usingwet and 12% using dry scrubber technologies. Wet scrubbers achievegreater than 90% SO_(x) removal efficiency compared to 80% by dryscrubbing. In wet scrubbers, the flue gas is brought into contact withslurry containing an alkaline source such as lime or limestone. TheSO_(x) is adsorbed into the water and reacts to form calcium sulfite. Ithas been demonstrated that simultaneous to SO_(x) capture, wet FGDs canbe used to capture vapor-phase mercury from the flue gas.

Elemental mercury is water-insoluble and is not removed by a wet FGD. Incontrast, oxidized mercury in the flue gas is water-soluble and isremoved. The Information Collection Request (ICR) mercury datademonstrated that ionic mercury is removed effectively approaching 90%by wet FGDs. Hence, one strategy for mercury capture is to oxidize allthe mercury during the burning of the coal and capture the oxidizedmercury in the wet scrubber. Work carried out by URS in conjunction withthe Department of Energy/National Energy Technology Laboratory(DOE/NETL) investigated just such a strategy. There are two criticaltechnical steps to the implementation of this strategy. The first is thecomplete oxidation of the vapor-phase mercury exiting the boiler and thecoal. URS, among others, is developing strategies and technologies toaccomplish this step. To date, they have demonstrated that independentof the coal type, vapor-phase mercury speciation can be shifted toextensively 100% oxidized mercury. The second critical technical step inthe implementation of this control strategy is the sorption of theoxidized mercury and removal in the wet scrubber. The problem,identified early on, is that there are reactions occurring in the wetscrubber liquor that reduce oxidized mercury to elemental mercury andlead to “re-emission” or release of elemental mercury into the scrubbedflue gas. The prevention of ionic mercury reduction in wet scrubberliquor has been studied and reported by G. M. Blythe and D. W. DeBerryat URS and others.

The findings have suggested that complexation of the ionic mercury isone way to reduce or eliminate the generation of elemental mercury inthe scrubber. This same study has demonstrated that not all chelants ofionic mercury can accomplish this in a wet FGD. In a recentpresentation, plant results of such a chelant, TMT-15,trimercapto-s-triazine, available from Degussa, were inconclusiveregarding the prevention of re-emission of mercury across a wetscrubber. Efficient and cost-effective apparatuses and methods forcontrolling emissions of mercury remain a desirable need in the artwhether from combustion sources such as coal plants and cement kilns orother sources such as incinerators used in a variety of activities.

SUMMARY

In one aspect, a method for reducing mercury emissions is disclosed. Inone embodiment, the method includes providing a gas stream comprisingmercury and passing the gas stream into a scrubber comprising a scrubberliquor and peracetic acid.

In one embodiment, the method includes burning a carbonaceous fuelcomprising mercury, thereby producing a flue gas, and passing the fluegas into a flue gas scrubber comprising a scrubber liquor and peraceticacid.

In some embodiments, the peracetic acid is mixed with a carrying agentselected from: limestone slurry, lime slurry, sodium-based alkalisolution, trona-based solution, sodium carbonate solution, sodiumhydroxide solution, and water.

In some embodiments, the method also includes mixing acetic acid and anoxidant to form the peracetic acid. In some embodiments, the oxidant isselected from hydrogen peroxide, sodium hypochlorite and mixtures of thesame. In some embodiments, the oxidant is hydrogen peroxide.

In some embodiments, the mercury is from combusted coal. In someembodiments, the mercury is from an incinerator. In some embodiments,the mercury is from a cement kiln. In some embodiments, the mercury isfrom an ore refinery. In some embodiments, the mineral ore processed atthe refinery contains phosphorus (such as phosphate). In someembodiments, the mineral ore processed at the refinery contains gold.

In some embodiments, the scrubber is a wet scrubber selected from aspray tower system, a jet bubbler system, and a co-current packed towersystem. In some embodiments, the peracetic acid is added to the liquorand then added to the scrubber. In some embodiments, the peracetic acidis added to the scrubber containing the liquor. In some embodiments, theperacetic acid is added to a virgin liquor then added to the scrubber.In some embodiments, the peracetic acid is added to a make-up liquorthen added to the scrubber. In some embodiments, the peracetic acid isadded to a return liquor then added to the scrubber. In someembodiments, the peracetic acid is added to a reclaimed liquor thenadded to the scrubber. In some embodiments, the peracetic acid is addedto a liquor injected directly into flue gases then added to thescrubber. In some embodiments, the peracetic acid is added to arecirculation loop of the scrubber liquor. In some embodiments, theperacetic acid is added to a low solids return to the scrubber from ascrubber purge stream. In some embodiments, the peracetic acid is addedto a demister. In some embodiments, the peracetic acid is added to amake-up water stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of an experimental setup of impingers tomeasure simulated mercury emission capture.

FIG. 2 shows the percentage of mercury removed from a flue gas using anembodiment of the invention at various peracetic acid concentrations.

DETAILED DESCRIPTION

Unless expressly stated to the contrary, use of the term “a” is intendedto include “at least one” or “one or more.” For example, “a device” isintended to include “at least one device” or “one or more devices.”

Any ranges given either in absolute terms or in approximate terms areintended to encompass both, and any definitions used herein are intendedto be clarifying and not limiting. Notwithstanding that the numericalranges and parameters setting forth the broad scope of the invention areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.Moreover, all ranges disclosed herein are to be understood to encompassany and all subranges (including all fractional and whole values)subsumed therein.

The present invention describes the use of peracetic acid tounexpectedly improve the capture of mercury emissions across a flue gasdesulfurizer (FGD) in coal-fired flue gas streams or other processingsystem where mercury vapor is present or released. Examples includemunicipal solid waste (MSW) incinerators, medical waste combustors, oreroaster and refineries and cement kilns.

The scrubbers currently used in the industry include spray towers, jetbubblers, and co-current packed towers as examples. These types of airpollution control devices (APCDs) are provided as examples and are notmeant to represent or suggest any limitation. The peracetic acid may beadded to virgin limestone or lime slurry prior to addition to thescrubber, the recirculation loop of the scrubber liquor, the “lowsolids” return to the scrubber from the scrubber purge stream, demisterwater, make-up water, or the scrubber liquor. Semi-dry FGDs can also beadapted, including spray dryer absorbers (i.e., SDAs), circulating dryscrubbers (CDS) or TURBBOSORP® available from Von Roll. The peraceticacid may be added to semi-dry FGDs so that the peracetic acid contactsmercury passing through the scrubber.

Typically, the peracetic acid is applied at a ratio of 0.5:1 to20000000:1 weight peracetic acid to weight of mercury being captured.The preferred ratio is from 1:1 to 2000000:1 and the most preferredrange is from 5:1 to 200000:1.

In some embodiments, the peracetic acid is generated by mixing aceticacid with an oxidant source. The oxidant source may be any agent capableof converting the acetic acid to peracetic acid. Examples of appropriateoxidant sources include hydrogen peroxide and sodium hypochlorite.

In general, peracetic acid may be introduced into the scrubber andthereby into the scrubber liquor via several routes. The following willserve as just some of the variations that are available to introduce theperacetic acid into the scrubber liquor. The scrubber liquor is definedas the water-based dispersion of calcium carbonate (limestone) orcalcium oxide (lime) used in a wet or dry flue gas scrubber to captureSO_(x) emissions. The liquor may also contain other additives such asmagnesium and low-molecular weight organic acids, which function toimprove sulfur capture. One example of such an additive is a mixture oflow-molecular weight organic acids known as dibasic acid (DBA). DBAtypically consists of a blend of adipic, succinic, and glutaric acids.Each of these organic acids can also be used individually. In addition,another low-molecular weight organic acid that can be used to improvesulfur capture in a wet scrubber is formic acid. Finally, the scrubberliquor will also contain byproducts of the interaction between the limeor limestone and flue gas, which leads to the presence of variousamounts of calcium sulfite or calcium sulfate as well as anions such ashalides (i.e., chlorides, bromides, and iodides) and other cations suchas iron, zinc, sodium, or copper. The scrubber liquor includes but isnot limited to the make-up liquor, return liquor, the reclaimed liquor,virgin liquor, and liquor injected directly into flue gases.

Another addition point for the peracetic acid to the wet scrubber is viathe “low solids” liquor return. A portion of the liquor is usuallycontinuously removed from the scrubber for the purpose of separatingreaction byproducts from unused lime or limestone. One means ofseparation that is currently used is centrifugation. In this process thescrubber liquor is separated into a “high solids” and “low solids”stream. The high solids stream is diverted to wastewater processing. Thelow solids fraction returns to the wet scrubber and can be consideredreclaimed dilute liquor. The peracetic acid can conveniently be added tothe reclaimed low solids stream prior to returning to the scrubber.

Another feed liquor found in the operation of a wet FGD is called“virgin liquor.” Virgin liquor is the water-based dispersion of eitherlime or limestone prior to exposure to flue gas and is used to add freshlime or limestone while maintaining the scrubber liquor level andefficiency of the wet FGD. This is prepared by dispersing the lime orlimestone in water. Here, the peracetic acid can be added either to thedispersion water or the virgin liquor directly or to the demister water.

Finally, some scrubber installations use scrubber liquor and/or water(fresh or recycled) injected directly into the flue gas prior to thescrubber for the purpose of controlling relative humidity of the fluegas or its temperature. The excess liquid is then carried into thescrubber. Here also are two potential addition points for theintroduction of the peracetic acid.

The addition of the peracetic acid can be made in any of theselocations, wholly or fractionally (i.e., a single feed point or multiplefeed points), including, but not limited to, the make-up water for thelime or limestone slurry or the scrubber liquor.

Often, the recovery of desirable ore products involves refining the orefrom materials that contain mercury. For example, phosphate is oftenextracted from phosphorite which contains mercury as a trace element.During refinement of the desirable phosphorous mineral, mercury can beliberated such during fertilizer manufacture. In such cases, the mercurypasses into a scrubber fluid, for example, a sodium-based alkali that isused to capture sulfur dioxide (SO₂). The mercury can be removed usingthe processes described herein.

As another example, gold ore processing often involves roasting the goldore to oxidize and remove sulfide. The gas generated by sulfur burningin the roaster is scrubbed to remove the sulfur dioxide and othercomponents which can be contaminated with mercury. Mercury can beremoved from these off-gases to make the gold processing moreenvironmentally desirable.

Thus, techniques described herein can be used to remove contaminatingamounts of mercury from off-gases arising from various ore processingand ore refineries processing those ores.

The invention is illustrated by the proceeding descriptions and thefollowing examples which are not meant to limit the invention unlessotherwise stated in the claims appended hereto.

EXAMPLES

Testing for elemental mercury oxidation or absorption was performedusing a multiple impinger setup with an inline mercury analyzer. Theinline mercury analyzer for this testing was an Ohio Lumex RA-915Portable Zeeman Mercury Analyzer.

Referring to FIG. 1, a multiple impinger setup (with impingers seriallyconnected: 1 to 2, 2 to 3, 3 to 4, etc.) was used to expose samples withelemental mercury. In Impinger 1, elemental mercury was added (200 ppt,5 mL) and combined with stannous chloride (2 mL) to evolve elementalmercury. In Impinger 2, 30 mL of solution was added. The solution can bea diluted sample, synthetic slurries, test slurries, deionized (DI)water (for calibration and reference) or any combination of the above.In Impingers 3-4, various solutions (30 mL) were added to reduce theamount of volatile material reaching the detector and not affect themercury signal. These various solutions included HNO₃ and NaOH solutionsat concentrations from 0.1 to 1M. During calibration, these materialsare replaced with the same volume of DI water. In the lastimpinger—Impinger 3, 4, or 5, depending on the system—was left empty tocatch any liquid overflow. The mercury detector was then connected tothe last impinger, followed by a carbon trap and pump. The pump drawsambient air from the room where the impingers are located.

The second impinger used for this application was not a typical bottomdraining impinger. Instead, a 100 mL round bottom flask was fitted atthe bottom of the impinger so that the flask could be lowered into aheating bath for variable temperature measurements and was large enoughfor a variety of test solution volumes. The solution was bubbled withgas through a disposable pipette.

Test slurries used were obtained from a commercial limestone forcedoxidation wet flue gas desulfurization scrubber at a coal-firedelectrical generator unit firing eastern bituminous coal. The pH of theslurry is typically between 5.5 and 6.5.

Example 1

Peracetic acid was tested as an additive to a test slurry. FIG. 2 showsthat the addition of peracetic acid to the test slurry drasticallyincreases the amount of flue gas elemental mercury captured by thewater-based liquor.

Mercury removal in FIG. 2 is calculated using the amount of elementalmercury not captured ([Hg⁰]_(NC), mercury detected at the detector)compared to the amount of mercury initially in the system ([Hg⁰]_(I)(Equation 1).

$\begin{matrix}{{{Hg}\mspace{14mu}{Removal}\;(\%)} = {\left( {1 - \frac{\left\lbrack {Hg}^{0} \right\rbrack_{NC}}{\left\lbrack {Hg}^{0} \right\rbrack_{I}}} \right) \times 100}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Comparative Example 1

Peroxysulfonated oleic acid was also added to the test slurry butresulted in mercury evolving from the solution (data not shown).

Comparative Example 2

To test the saturation of elemental mercury in water, a known amount ofelemental mercury vapor was bubbled through deionized water in a plasticjug using a Mercury Instruments MC-3000 Mercury Calibrator. A mercurygenerator was employed to create vapor phase elemental mercury (29 or270 μg/m³) with a N₂ carrier gas (2.5 L/min). This gaseous mixture wasthen bubbled through deionized water (0.9 L) for a varying amount oftime (1-20 min). A small amount of water was then removed for analysison an Ohio Lumex RA-915 Portable Zeeman Mercury Analyzer.

The retention of elemental mercury in water over time was also testedusing the same testing setup and procedure as above with one addition.After bubbling mercury through the deionized water for a set amount oftime, the mercury ampule was bypassed so that only N₂ gas would flowthrough the deionized water.

Elemental mercury was bubbled through deionized water to determine thesaturation of elemental mercury in a system more similar to the dynamicsystem in a wet flue gas desulfurizer scrubber. The results shown inTable I indicate that the system was driving towards a steady state of˜60 ppt and ˜700 ppt, at 29 μg/m³ and 270 μg/m³ respectively, ratherthan increasing up to the saturation limit of 60 ppb (60,000 ppt) all at25° C. The initial concentrations at short times are higher thanexpected due to an oversaturation of the nitrogen carrier gas in thehead space of the mercury ampoule, causing a burst of elemental mercuryat the beginning of each test. Over time in both the low and highconcentration systems, the concentration of elemental mercury drives toan equilibrium value. The theoretical values in Table I refer to thetotal amount of elemental mercury flow through the testing system basedon concentration, flow rate and time.

TABLE I Gas: 29 μg/m³ and 2.5 L/min Gas: 270 μg/m³ and 2.5 L/min ElapseElapse Time Hg⁰ in water, (ppt) Time Hg⁰ in water, (ppt) (min)Theoretical* Actual (min) Theoretical* Actual 1.0 146 235 1 349 601 2.5309 137 10 6,139 701 5.0 521 93 20 21,139 667 10.0 937 61 15.0 1,342 58

The saturation of elemental mercury in water was driving to equilibriumas governed by Henry's Law (Equation 2 below). Henry's law is defined asHenry's constant (K_(H), 376 atm at 25° C.), mole fraction of elementalmercury in solution (x), and partial pressure of elemental mercury (p,atm). Below in Table II are the theoretical values of elemental mercuryin water based on Henry's Law and the concentration of the gas flowingthrough the system. The values are not exactly the same as the actualmeasured values but are on the same order of magnitude. Thesepredictions are significantly lower than the solubility limit of 60 ppbfor elemental mercury in pure water.

$\begin{matrix}{K_{H} = \frac{p}{x}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

TABLE II Elemental Mercury Concentration Gas Phase Water Phase (ppt)(μg/m³) Actual Theoretical* 29 60 103 270 700 963 0.3 — 2 5.0 — 1816,823 — 60,000

Next, these same solutions were tested for mercury retention orstability by first adding elemental mercury to the water in the samemanner as above and then bypassing the elemental mercury ampoule so thatonly N₂ gas (elemental mercury content of zero) bubbles through thewater for a varying amount of time. This would approximate the effect ofa forced oxidation system in the wet flue gas desulfurizer scrubbers. InTable III, it can be seen that the elemental mercury was quickly removedfrom the deionized water by the pure N₂ gas. This behavior is alsoconsistent with Henry's Law as the elemental mercury in the water phasetransfers to the gas phase, the system continuously shifts in order toreach equilibrium. Elemental mercury was not readily soluble or retainedin deionized water.

TABLE III 29 μg/m³ at 2.5 L/min for 1 min 270 μg/m³ at 2.5 L/min for 1min N₂ flow N₂ flow % time (min) Hg (ppt) % retention time (min) Hg(ppt) retention 0 297 0 601 1 174 59% 1 374 62% 2.5 71 24% 2.5 157 26% 514 5% 5 35.7 6% 29 μg/m³ at 2.5 L/min for 10 min 270 μg/m³ at 2.5 L/minfor 10 min N₂ flow N₂ flow % time (min) Hg (ppt) % retention time (min)Hg (ppt) retention 0 76 0 701 1 46 61% 1 439 63% 2.5 18 24% 5 90 13% 53.4 4% 10 5.4 1%

The data in these tables clearly define the problem by demonstratingthat water-based scrubber liquors do not effectively decrease elementalmercury concentration in combustion flue gas.

These bench-scale results shown in Table IV and FIG. 2 demonstrate thatthe peracetic acid compound successfully and unexpectedly controls theemission of mercury from a scrubber by decreasing the elemental mercuryflue gas concentration and does so more efficiently than conventionaltechniques.

TABLE IV Elemental Elemental Peracetic Mercury Activated Mercury AcidRetention Carbon Retention (ppm) (%) (ppm) (%) 100 98% 100 12% 50 88% —— 10 97% — — 0  5% — —

Example 2

Using an experimental reticulating slurry system, elemental mercury (˜11μg/m³ in N₂) was bubbled through a 1 L solution of deionized water orWFGD slurry sample from a power plant in a large impinger. Peraceticacid was added at a rate of 50 ppm/hour to the basin of the system whichfed area being fed to the impinger. Elemental mercury was continuouslymonitored at the output of the system. To the elemental mercury gasstream SO₂ was also added at 100 ppm for some tests.

TABLE V SO₂ Elemental Mercury Concen- Removal (%) tration DI WFGD (ppm)water Slurry 0  0% 32% 100 64% 91%

Table V includes data from peracetic acid addition to deionized waterand slurry at 50 ppm/hour. Included is data with and without SO₂incorporated into the elemental mercury gas stream.

The presence of SO₂ in the elemental mercury gas stream of solutionscontaining peracetic acid for elemental mercury removal see asynergistic increase in elemental mercury removal. Even in systems whereno elemental mercury removal was previously seen (DI water), theaddition of SO₂ to the gas stream greatly increased the amount ofelemental mercury removed by systems containing peracetic acid.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the invention and withoutdiminishing its intended advantages. It is therefore intended that suchchanges and modifications be covered by the appended claims.

What is claimed is:
 1. A method for reducing mercury emissions,comprising: providing a gas stream comprising mercury; passing the gasstream into a scrubber comprising a scrubber liquor, peracetic acid, andhydrogen peroxide, wherein the peracetic acid is mixed with a carryingagent selected from the group consisting of a lime slurry, asodium-based alkali solution, a trona-based solution, a sodium carbonatesolution, a sodium hydroxide solution, water, and any combinationthereof, and removing the mercury from the gas stream, wherein theperacetic acid is applied at a ratio of 5:1 to 200000:1 weight theperacetic acid to weight of the mercury being captured.
 2. The method ofclaim 1, wherein the carrying agent is water.
 3. The method of claim 1,wherein the mercury is from combusted coal.
 4. The method of claim 1,wherein the scrubber is a wet scrubber selected from a spray towersystem, a jet bubbler system, and a co-current packed tower system. 5.The method of claim 1, wherein the peracetic acid is added to the liquorand then added to the scrubber.
 6. The method of claim 1, wherein theperacetic acid is added to the scrubber containing the liquor.
 7. Themethod of claim 1, wherein the peracetic acid is added to a virginliquor then added to the scrubber.
 8. The method of claim 1, wherein theperacetic acid is added to a make-up liquor then added to the scrubber.9. The method of claim 1, wherein the peracetic acid is added to areturn liquor then added to the scrubber.
 10. The method of claim 1,wherein the peracetic acid is added to a reclaimed liquor then added tothe scrubber.
 11. The method of claim 1, wherein the peracetic acid isadded to a liquor injected directly into flue gases then added to thescrubber.
 12. The method of claim 1, wherein the peracetic acid is addedto a recirculation loop of the scrubber liquor.
 13. The method of claim1, wherein the peracetic acid is added to a low solids return to thescrubber from a scrubber purge stream.
 14. The method of claim 1,wherein the peracetic acid is added to an aqueous stream introduced intothe scrubber, wherein the aqueous stream is selected from a demister andmake-up water stream.
 15. The method of claim 1, wherein the mercury isfrom an incinerator, cement kiln, or an ore refinery.
 16. The method ofclaim 1, wherein the peracetic acid is not added directly to thescrubber.
 17. The method of claim 1, wherein the peracetic acid is addedin an amount of about 10 ppm to about 100 ppm.